Chih-Chun Wang, Ness B. Shroff. Beyond the Butterfly - A Graph-Theoretic Characterization of the Feasibility of Network Coding with Two Simple Unicast Sessions. In IEEE International Symposium on Information Theory, ISIT 2007, Nice, France, June 24-29, 2007. pages 121-125, IEEE, 2007. [doi]
Abstract is missing.